1. Field of the Invention
The present invention relates to a top spin valve sensor that has an iridium manganese (IrMn) pinning layer and an iridium manganese oxide (IrMnO) seed layer and, more particularly, to such a top spin valve sensor which has an improved magnetoresistive coefficient even though the iridium manganese (IrMn) pinning layer is formed by ion beam sputter deposition.
2. Description of the Related Art
A spin valve sensor is employed by a read head for sensing magnetic signal fields from a moving magnetic medium, such as a rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning a magnetic moment of the pinned layer 90xc2x0 to an air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the magnetic disk. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. A magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or bias point position in response to positive and negative magnetic field signals from a rotating magnetic disk. The quiescent position, which is preferably parallel to the ABS, is the position of the magnetic moment of the free layer with the sense current conducted through the sensor in the absence of field signals.
The thickness of the spacer layer is chosen so that shunting of the sense current and a magnetic coupling between the free and pinned layers are minimized. This thickness is typically less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons are scattered at the interfaces of the spacer layer with the pinned and free layers. When the magnetic moments of the pinned and free layers are parallel with respect to one another scattering is minimal and when their magnetic moments are antiparallel scattering is maximized. Changes in scattering changes the resistance of the spin valve sensor as a function of cos xcex8, where xcex8 is the angle between the magnetic moments of the pinned and free layers. The sensitivity of the sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in the resistance of the sensor as the magnetic moment of the free layer rotates from a position parallel with respect to the magnetic moment of the pinned layer to an antiparallel position with respect thereto and R is the resistance of the sensor when the magnetic moments are parallel.
A read head in a magnetic disk drive of a computer includes the spin valve sensor as well as nonconductive nonmagnetic first and second read gap layers and ferromagnetic first and second shield layers. The spin valve sensor is located between the first and second read gap layers and the first and second read gap layers are located between the first and second shield layers. In the construction of the read head the first shield layer is first formed followed by formation of the first read gap layer, the spin valve sensor, the second read gap layer and the second shield layer. Spin valve sensors are classified as a top or a bottom spin valve sensor depending upon whether the pinning layer is located at the bottom of the sensor next to the first read gap layer or at the top of the sensor closer to the second read gap layer. Spin valve sensors are further classified as simple pinned or antiparallel pinned depending upon whether the pinned layer structure is one or more ferromagnetic layers with a unidirectional magnetic moment or a pair of ferromagnetic layers that are separated by a coupling layer with magnetic moments of the ferromagnetic layers being antiparallel.
The storage capacity of a magnetic disk drive in a computer is directly dependent upon the areal density of each of the write head and the read head. When the areal density is increased the storage capacity of the computer is increased. Areal density is a product of the linear bit density and track width density. Linear bit density is measured in bits per inch (BPI) along a track of a magnetic disk and the track width density is measured in tracks per inch (TPI) across the width of the tracks on the magnetic disk. The linear bit density of a read head is determined by the spacing between the first and second shield layers. This spacing, in turn, is dependent upon the thickness of the spin valve sensor and the first and second read gap layers. When this thickness increases the linear bit density decreases. Accordingly, it is highly desirable that the distance between the first and second shield layers be minimized.
The thickest layer in a spin valve sensor is typically the pinning layer. For instance, a nickel manganese pinning layer must be about 250 xc3x85 in order to pin the pinned layer, a platinum manganese (PtMn) pinning layer must be about 180 xc3x85 in order to pin the pinned layer and a nickel oxide (NiO) pinning layer must be about 425 xc3x85 in order to pin the pinning layer. An exceptionally thin pinning layer, which is capable of pinning the pinned layer with only the thickness of 60 xc3x85, is iridium manganese (IrMn). While this pinning layer is highly desirable from the standpoint of reducing the read gap between the first and second shield layers, the magnetoresistive coefficient dr/R of the sensor has been relatively low when the iridium manganese (IrMn) pinning layer is formed by ion beam sputter deposition. Ion beam sputter deposition is a highly desirable method of forming layers of a spin valve sensor because its yield is significantly greater than standard sputter deposition techniques. Accordingly, it would be desirable if iridium manganese (IrMn) could be used as a pinning layer, provided the read head had a relatively high magnetoresistive coefficient dr/R when the pinning layer is formed by ion beam sputter deposition. It should be noted that when the magnetoresistive coefficient dr/R is increased that the linear bit density is still further increased since the read head has an improved read signal and can read more bits per linear inch along the track.
The present invention has provided a read head with improved magnetoresistive coefficient dr/R even though an iridium manganese (IrMn) pinning layer has been formed by ion beam sputter deposition. This has been accomplished in a top spin valve sensor by providing a seed layer of iridium manganese oxide (IrMnO) between the first read gap layer and the free layer. Without the seed layer the magnetoresistive coefficient was found to be between 6% and 7%, in one embodiment of the invention with the iridium manganese oxide (IrMnO) seed layer the magnetoresistive coefficient dr/R was increased to 7.4% and in a second embodiment of the invention with the iridium manganese oxide (IrMnO) seed layer the magnetoresistive coefficient dr/R was significantly increased to 8.65%.
An object of the present invention is to provide a read head with improved magnetoresistive coefficient dr/R when a spin valve in the read head has an iridium manganese (IrMn) pinning layer which has been formed by ion beam sputter deposition.
Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings.